Method of copper/copper surface bonding using a conducting polymer for application in IC chip bonding

ABSTRACT

A semiconductor chip having an exposed metal terminating pad thereover, and a separate substrate having a corresponding exposed metal bump thereover are provided. A conducting polymer plug is formed over the exposed metal terminating pad. A conforming interface layer is formed over the conducting polymer plug. The conducting polymer plug of the semiconductor chip is aligned with the corresponding metal bump. The conforming interface layer over the conducting polymer plug is mated with the corresponding metal bump. The conforming interface layer is thermally decomposed, adhering and permanently attaching the conducting polymer plug with the corresponding metal bump. Methods of forming and patterning a nickel carbonyl layer are also disclosed.

[0001] This application is a Continuation-in-Part of application Ser.No. 09/612,576 filed on Jul. 7, 2000 and assigned to a common assignee.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the packaging ofsemiconductor devices, and more specifically to copper interconnectprocesses between chips and substrates in packaging processes.

BACKGROUND OF THE INVENTION

[0003] Recent integration of copper interconnect processes into IC(integrated circuit) manufacturing requires copper terminating chips tobe bonded directly on the copper metal pad and circuit boards. Thepresent invention allows the use of conducting polymers to bond copperterminating chips directly on copper substrate or printed circuitboards.

[0004] U.S. Pat. No. 5,923,955 to Wong describes a process for creatinga flip-chip bonded combination for a first and second integratedcircuits using a Ni/Cu/TiN structure.

[0005] U.S. Pat. No. 5,891,756 to Erickson describes a method forforming a solder bump pad, and specifically to converting a wire bondpad of a surface-mount IC device to a flip-chip solder bump pad suchthat the IC device can be flip-chip mounted to a substrate. The methoduses a Ni layer over the pad.

[0006] U.S. Pat. No. 5,795,818 to Marrs describes a method of forming aninterconnection between bonding pads on an integrated circuit chip andcorresponding bonding contacts on a substrate. The method uses coinedball bond bumps.

[0007] U.S. Pat. No. 5,904,859 to Degani describes a method for applyingunder bump metallization (UBM) for solder bump interconnections oninterconnection substrates. The UBM comprises a Cu, Cu/Cr, Cr multilayerstructure.

[0008] U.S. Pat. No. 5,767,009 to Yoshida et al. describes a method ofreducing cross talk noise between stacked semiconductor chips by the useof a chip on chip mounting structure.

[0009] U.S. Pat. No. 5,804,876 to Lake et al. describes a low contactresistance electrical bonding interconnect having a metal bond padportion and conductive epoxy portion.

SUMMARY OF THE INVENTION

[0010] Accordingly, it is an object of the present invention is toprovide a method of bonding a chip to a substrate without the need for abump metal, wetting agents, and barrier materials.

[0011] Another object of the present invention is to provide a method ofbonding a chip to a substrate avoiding the use of environmentallyunfriendly solder and solder material.

[0012] An additional object of the present invention is to provide amethod of bonding a chip to a substrate in smaller micron scale metalpitch sizes.

[0013] Other objects will appear hereinafter.

[0014] It has now been discovered that the above and other objects ofthe present invention may be accomplished in the following manner.Specifically, a semiconductor chip having an exposed metal terminatingpad thereover, and a separate substrate having a corresponding exposedmetal bump thereover are provided. A conducting polymer plug is formedover the exposed metal terminating pad. A conforming interface layer isformed over the conducting polymer plug. The conducting polymer plug ofthe semiconductor chip is aligned with the corresponding metal bump. Theconforming interface layer over the conducting polymer plug is matedwith the corresponding metal bump. The conforming interface layer isthermally decomposed, adhering and permanently attaching the conductingpolymer plug of the semiconductor chip with the corresponding metal bumpof the separate substrate. Methods of forming and patterning a nickelcarbonyl layer are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The features and advantages of the present invention will be moreclearly understood from the following description taken in conjunctionwith the accompanying drawings in which like reference numeralsdesignate similar or corresponding elements, regions and portions and inwhich:

[0016] FIGS. 1 to 6 schematically illustrate in cross-sectionalrepresentation a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Unless otherwise specified, all structures, layers, etc. may beformed or accomplished by conventional methods known in the prior art.

[0018] Accordingly, as shown in FIG. 1, semiconductor structure 200includes an overlying final metal layer 212 connected to, for example,metal line 214 through metal via 216. Metal terminating pad 218 overliesfinal metal layer 212 at a predetermined position within firstpassivation layer 220.

[0019] Semiconductor structure 200 is understood to possibly include asemiconductor wafer or substrate, active and passive devices formedwithin the wafer, conductive layers and dielectric layers (e.g.,inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed overthe wafer surface. The term “semiconductor structure 200” is meant toinclude a semiconductor chip.

[0020] Final metal layer 212 and metal terminating pad 218 arepreferably comprised of copper as will be used for illustrative purposeshereafter.

[0021] Additional metal vias 216, metal lines 214, metal terminatingpads 218, etc., may be formed within and over semiconductor structure200 although for purposes of illustration, only single such structuresare shown in FIGS. 11. For purposes of simplicity, metal via 216, metalline 214, and final metal layer 212 are not explicitly illustrated inthe following FIGS. 2-6.

[0022] Final passivation layer 222 is formed over first passivationlayer 220 and copper terminating pad 218 to a thickness of from about1000 to 10,000 Å, and more preferably from about 2000 to 5000 Å.

[0023] Opening 224 is formed within second passivation layer 222exposing copper terminating pad 218.

[0024] As shown in FIG. 2, planarized conducting polymer plug 250 isformed within opening 224 by flowing or using a spin-on-technique oncopper surfaces such a bonding pads 218 or copper tracks on printedcircuit boards. Planarized conducting polymer plug 250 is preferablyfrom about 1000 to 10,000 Å thick, and more preferably from about 3000to 6000 Å thick.

[0025] Conducting polymer plug 250 includes, but is not restricted todoped polyacetylene, poly (para-phenylene vinylene) (PPV), orpolyaniline manufactured by DuPont, Ciba Geigy, and Sieman's and others.

[0026] Conducting polymer plug 250 is used to achieve an effectivecopper/copper surface bonding in copper terminating IC chip pads 218.The conducting polymer has good conductive properties, is highly dopedto degeneracy (see below), has good adhesive properties and very usefulthermal insulation properties.

[0027] The main characteristics of the conducting polymer formingconducting polymer plug 250 is the presence of the so-called conjugatedchain where the chemical bonding between the atoms in the mainly carbon“backbone” of the polymer chain alternates between single and doublebonds.

[0028] There are two types of bonds namely the omega-bond and thephi-bond. Electrons in the former (omega-bond) are strongly localizedand form strong bonds, in contrast to the later (phi-bond) in which theelectrons form weak bonds and are not localized.

[0029] The electrons in phi-bonds can be thought of a cloud that extendsalong the entire length of the conjugated chain in which electrons arefree to move in a similar fashion to conducting electrons in a metal.The conducting polymer is heavily doped to achieve a conduction which iscomparable to a degenerate semiconductor and is sufficient enough not toperturb the device performance.

[0030] As shown in FIG. 3, interface layer 260 is formed over secondpassivation layer 222 and conducting polymer plug 250. Interface layer260 is preferably comprised of nickel carbonyl (Ni(CO)₄) as will be usedfor illustrative purposes hereafter. The material for interface layer isselected to be subject to thermal decomposition be chemical combustible.

[0031] Ni(CO)₄ has a freezing point of −19° C., between −19° C. and 40°C. nickel carbonyl exists as a liquid and, at temperatures above 40° C.,the following reaction takes place:

Ni(CO)₄→Ni+4CO

[0032] Below 40° C., the reverse reaction takes place:

Ni+4CO→Ni(CO)₄

[0033] Two methods may be used to form Ni(CO)₄ interface layer 260. Inthe first method, nickel is first deposited (through sputtering orelectroplating) over second passivation layer 222 and conducting polymerplug 250. Then, carbon monoxide (CO) is introduced into the reactionchamber and reacts with the deposited nickel layer to form Ni(CO)₄interface layer 260. The CO may be pressurized as necessary. Thetemperature of the chamber and/or the temperature of the wafer must beless than 40° C. to form the Ni(CO)₄ and then keep below −19° C. tomaintain the Ni(CO)₄ interface layer 260 as a solid.

[0034] In the second method, liquid Ni(CO)₄ (at a temperature between−19° C. and 40° C.) is flowed over second passivation layer 222 andconducting polymer plug 250 and then the temperature of the chamberand/or the temperature of the wafer is lowered to less than −19° C. soas to convert the liquid Ni(CO)₄ into solid Ni(CO)₄ interface layer 260.

[0035] Regardless of which method is used, the temperature of thechamber and/or the temperature of the wafer must be less than −19° C. tomaintain the Ni(CO)₄ interface layer 260 as a solid.

[0036] As shown in FIG. 4, the excess of Ni(CO)₄ interface layer 260 notover conducting polymer plug 250 is removed to form conforming Ni(CO)₄interface layer 260′ over conducting polymer plug 250. To remove theexcess of Ni(CO)₄ interface layer 260 not over conducting polymer plug250, a partial chrome photomask (not shown) is formed over the waferwith the chrome portion of the photomask overlying that portion of theNi(CO)₄ interface layer 260 overlying the conducting polymer plug 250.The partial chrome photomask is then subjected to a radiation sourcesuch that radiation penetrates the photomask to the Ni(CO)₄ interfacelayer 260 not over conducting polymer plug 250 and raising thetemperature of that portion of the Ni(CO)₄ interface layer 260 above 40°C. so that the reaction

Ni(CO)₄→Ni+4CO

[0037] takes place, removing the Ni(CO)₄ interface layer 260 not overconducting polymer plug 250. No radiation may penetrate the chromeportion of the photomask overlying the Ni(CO)₄ interface layer 260 overconducting polymer plug 250 so that portion of the Ni(CO)₄ interfacelayer 260 remains as Ni(CO)₄.

[0038] Final passivation layer 222 is also then removed, exposingconducting polymer plug 250 with overlying conforming Ni(CO)₄ interfacelayer 260′. As shown in FIG. 5, pre-formed metal bump 300 (connected tometal track 310 within substrate 320) is aligned, mechanically pressed,and mated with, conducting polymer plug 250 with overlying conformingNi(CO)₄ interface layer 260′. Substrate 320 may be a bond pad or aprinted circuit board, for example.

[0039] Metal bump 300 and metal track 310 are preferably comprised ofcopper as will be used for illustrative purposes hereafter. Cu metalbump 300 is formed by electroless plating, at about 200° C.

[0040] As shown in FIG. 6, conforming Ni(CO)₄ interface layer 260′thermally decomposes allowing copper bump 300 to adhere directly withconducting polymer plug 250 at temperature above about 40° C.:

Ni(CO)₄→Ni+4CO

[0041] With slight application of pressure, the thermal decomposition ofNi(CO)₄ interface layer 260′ facilitates Ni bonding of copper bump 300to conducting poly plug 250.

[0042] The present invention may find wide application in flip-chip,chip-on-board, and micron metal bonding and provides for micron scalebonding.

[0043] Thus, the present invention permits semiconductor chips withcopper interconnect termination to be directly bonded by a flip-chip,chip-on-board, and micron metal bonding processes onto a coppersubstrate or printed circuit board, eliminating the need for a bumpmetal, wetting agent metals and barrier materials with the attendantcostly process steps and materials involved. It further avoids the useof environmentally unfriendly solder and solder materials, and allowsfor use in smaller micron scale metal pitch sizes unlike most of thecurrent bonding techniques.

[0044] While particular embodiments of the present invention have beenillustrated and described, it is not intended to limit the invention,except as defined by the following claims.

We claim:
 1. A method of bonding a chip to a substrate, comprising thesteps of: providing a semiconductor chip having an exposed metalterminating pad thereover, and a separate substrate having acorresponding exposed metal bump thereover; forming a conducting polymerplug over said exposed metal terminating pad; forming a conforminginterface layer over said conducting polymer plug; aligning saidconducting polymer plug of said semiconductor chip with saidcorresponding metal bump; mating said conforming interface layer oversaid conducting polymer plug with said corresponding metal bump; andthermally decomposing said conforming interface layer, adhering andpermanently attaching said conducting polymer plug of said semiconductorchip with said corresponding metal bump of said separate substrate. 2.The method of claim 1, wherein said conducting polymer plug is fromabout 1000 to 10,000 Å thick.
 3. The method of claim 1, wherein saidexposed metal terminating pad and said exposed metal bump are comprisedof copper.
 4. The method of claim 1, wherein said conducting polymerplug is comprised of a material selected from the group consisting ofdoped polyacetylene, poly (para-phenylene vinylene) (PPV), andpolyaniline.
 5. The method of claim 1, wherein said conducting polymerplug is a material doped to degeneracy.
 6. The method of claim 1,wherein said conforming interface layer is comprised of Ni(CO)₄.
 7. Amethod of bonding a chip to a substrate, comprising the steps of:providing a semiconductor chip having a metal terminating pad thereover,and a separate substrate having a corresponding exposed metal bumpthereover; forming final passivation layer over said metal bump; formingan opening within said final passivation layer, exposing said metalterminating pad; forming a conducting polymer plug within said finalpassivation layer opening and over said exposed metal terminating pad;forming an interface layer over said conducting polymer plug and saidfinal passivation layer; removing the excess of said interface layerover said final passivation layer and not over said conducting polymerplug, forming conforming interface layer; removing said passivationlayer from said semiconductor chip; aligning said conducting polymerplug of said semiconductor chip with said corresponding metal bump;mating said conforming interface layer over said conducting polymer plugwith said corresponding metal bump; and thermally decomposing saidconforming interface layer, adhering and permanently attaching saidconducting polymer plug of said semiconductor chip with saidcorresponding metal bump of said separate substrate.
 8. The method ofclaim 7, wherein said conducting polymer plug is from about 1000 to10,000 Å thick.
 9. The method of claim 7, wherein said exposed metalterminating pad and said exposed metal bump are comprised of copper. 10.The method of claim 7, wherein said conducting polymer plug is comprisedof a material selected from the group consisting of doped polyacetylene,poly (paraphenylene vinylene) (PPV), and polyaniline.
 11. The method ofclaim 7, wherein said conducting polymer plug is doped to degeneracy.12. The method of claim 7 wherein said conforming interface layer iscomprised of Ni(CO)₄.
 13. A method of bonding a chip to a substrate,comprising the steps of: providing a semiconductor chip having a copperterminating pad thereover, and a separate substrate having acorresponding exposed copper bump thereover; forming final passivationlayer over said copper bump; forming an opening within said finalpassivation layer, exposing said copper terminating pad; forming aconducting polymer plug within said final passivation layer opening andover said exposed copper terminating pad; said conducting poly plugbeing from about 1000 to 10,000 Å thick; forming an interface layer oversaid conducting polymer plug and said final passivation layer; removingthe excess of said interface layer over said final passivation layer andnot over said conducting polymer plug, forming conforming interfacelayer; removing said passivation layer from said semiconductor chip;aligning said conducting polymer plug of said semiconductor chip withsaid corresponding copper bump; mating said conforming interface layerover said conducting polymer plug with said corresponding copper bump;and thermally decomposing said conforming interface layer, adhering andpermanently attaching said conducting polymer plug of said semiconductorchip with said corresponding copper bump of said separate substrate. 14.The method of claim 13, wherein said conducting polymer plug is fromabout 3000 to 6000 Å thick.
 15. The method of claim 13, wherein saidconducting polymer plug is comprised of a material selected from thegroup consisting of doped polyacetylene, poly (para-phenylene vinylene)(PPV), and polyaniline.
 16. The method of claim 13, wherein saidconducting polymer plug is doped to degeneracy.
 17. The method of claim13 wherein said conforming interface layer is comprised of Ni(CO)₄. 18.A method of forming a Ni(CO)₄ layer, comprising the steps of: providinga substrate within a reaction chamber; forming a layer of nickel overthe substrate; and introducing CO into the reaction chamber at atemperature of less than 40° C. to cause the reaction Ni+4CO→Ni(CO)₄  tooccur whereby the Ni(CO)₄ layer is formed.
 19. The method of claim 18,wherein the nickel layer is formed by sputtering or electroplating. 20.The method of claim 18, wherein the CO introduced into the reactionchamber is pressurized.
 21. The method of claim 18, wherein the nickellayer is formed by sputtering or electroplating; and the CO introducedinto the reaction chamber is pressurized.
 22. The method of claim 18,wherein the formed Ni(CO)₄ layer is maintained below −19° C. whereby theformed Ni(CO)₄ layer is solid.
 23. The method of claim 18, wherein thesubstrate is a semiconductor substrate.
 24. The method of claim 18,wherein the nickel layer is formed by sputtering or electroplating; theCO introduced into the reaction chamber is pressurized; and substrate isa semiconductor substrate.
 25. A method of forming a solid Ni(CO)₄layer, comprising the steps of: providing a substrate within a reactionchamber; forming a liquid layer of Ni(CO)₄ over the substrate at atemperature between −19° C. and 40° C.; and then lowering thetemperature of the substrate or the reaction chamber below −19° C. toform the solid Ni(CO)₄ layer.
 26. The method of claim 25, wherein thesubstrate is a semiconductor substrate.
 27. A method of patterning asolid Ni(CO)₄ layer, comprising the steps of: providing a substratehaving a solid Ni(CO)₄ layer formed thereover; forming a partial chromephotoresist layer over the solid Ni(CO)₄ layer; the partial chromephotoresist having a chrome portion and a non-chrome portion; exposingthe partial chrome photoresist layer with radiation that penetrates onlythe non-chrome portion of the photoresist layer to the underlying solidNi(CO)₄ layer whereby the temperature of the radiation exposed portionof the solid Ni(CO)₄ layer is increased to above 40° C. so that theradiation exposed portion of the solid Ni(CO)₄ layer decomposes so thatthe solid Ni(CO)₄ layer is patterned.
 28. The method of claim 27,whereby the solid Ni(CO)₄ layer decomposes according to the reaction:Ni(CO)₄→Ni+4CO.
 29. The method of claim 27, whereby the solid Ni(CO)₄layer has a temperature of less than −19° C.
 30. The method of claim 27,whereby the solid Ni(CO)₄ layer has a temperature of less than −19° C.;and the solid Ni(CO)₄ layer decomposes above 40° C. according to thereaction: Ni(CO)₄→Ni+4CO.